1. Field of the Invention
The present invention relates to a method for the production of single crystalline MgTiO3 flakes, to single crystalline MgTiO3 flakes produced by this method as well as to the use thereof, in particular as pigments.
2. Description of the Related Art
Inorganic pigments such as mica, talc, glass flakes, MIO (micaceous iron oxide) and so on have been used for a long time in formulations such as paints, films, coating compositions and cosmetics for several purposes, either coated or uncoated.
In addition to the usually used inorganic particles as mentioned above, titanate particles have been proven to be useful for several purposes in coatings and compositions. Titanates exhibit electrical properties such as piezoelectricity and conductivity, mechanical properties such as abrasion-extinguishing and reinforcing, as well as chemical properties such as hydrophilicity and surface activity. By now, titanates are used in various applications such as ceramic capacitors, photocatalysts, semiconductors and electrode materials. As the titanates, potassium titanate, barium titanate, strontium titanate, calcium titanate, magnesium titanate, lead titanate, aluminum titanate and lithium titanate are of particular interest.
Titanate powders which are composed of flaky titanate particles are in their dispersibility and orientation behavior comparable to classic inorganic pigments like mica or talc which exhibit a naturally excellent dispersibility and orientation based on the flaky shape thereof. Therefore, titanate flakes are desired which might be used as pigments and bulking agents.
For example, Japanese Unexamined Patent Application Publication No. 05-163117 (Patent Document 1) discloses flakes of polycrystalline potassium hexatitanate (K2Ti6O13) which either contain color imparting metal ions or are coated with a metal oxide and are used as extender pigment or coloring pigment. The process for the production of the polycrystalline flakes needs at least two heating steps with temperatures above about 500° C.
Japanese Unexamined Patent Application Publication No.2008-162971 (Patent Document 2) discloses platy titanate crystal particles (K3xLixTi2−xO4, K2xMgxTi2−xO4, or KxFexTi2−xO4 , with 0.05≤x≤0.5 in every case) of the lepidocrocite type which exhibit a particular size range and are produced by a flux growth process, as well as their use as bright pigment and bulking agent. Here too, the process for the production of the platy titanate particles includes at least two heating steps with temperatures of ≥800° C.
The production methods described in these Patent Documents need to be improved further from the view point of efficiency.
For example, potassium hexatitanate (K2Ti6O13) flakes obtained by the method described in Patent Document 1 are polycrystalline. Therefore, their refractive index is lower than for a single crystalline titanate of the same composition. Furthermore, the requirement of one high temperature heat melting step and one high temperature calcination step takes time, is costly and causes more complications in the production process.
Similar thereto, the production process for the lepidocrocite type platy titanate crystal particles obtained by the method described in Patent Document 2 does also require two high temperature calcination steps which take time, are costly and cause more complications in the producing step.
The present inventors focused on magnesium titanate which has good dielectric properties, biocompatibility and exhibits anisotropic thermal expansion, and developed a process for the production of magnesium titanate particles which might be used in several usual pigment applications.
The aim of the present invention is to offer a production method having reduced energy cost and, thus, offering a method to effectively produce single crystalline MgTiO3 flakes suitable for use as pigments in various applications, to offer magnesium titanate single crystalline flakes produced by this method as well as to show how they may be used.